Apparatus and method for spray-painting

ABSTRACT

Spray-painting apparatus and method in which provision is made for: an inlet for the air under pressure (AIR IN); a heating unit (G 1 ) for the compressed air; an air drying/separation unit (G 2 ) consisting of hollow-fibre membranes; means ( 3, 15, 16 ) to adjust heating of the treated air; means ( 13 ) to adjust pressure of the treated air; means ( 10, 19 ) for adjusting either the dew point or the percentage of oxygen in the treated air in the case of hollow-fibre membranes for nitrogen separation; an outlet for the treated air (AIR OUT)to be used as paint carrier fluid.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a membrane apparatus fortreatment of compressed air and production of dried air or,alternatively, modified nitrogen-rich air, which are free fromimpurities and have a high degree of drying, and in particular to aspray-painting apparatus using treated compressed air as a carrier fluidin spray-painting.

[0003] The invention offers the possibility of varying the exittemperature on use, in particular of the compressed dry air or modifiednitrogen-rich air used as a carrier fluid in spray-painting devices.

[0004] 2. Prior Art

[0005] It is known that spray-painting devices of known type consist ofguns or nozzles, into which a flow of air under pressure (about 3-5bars) and a supply of the paint to be sprayed are conveyed.

[0006] The air acts as a vector, entraining the paint therewith andtransferring it to the surface to be painted.

[0007] Applicative examples of spray painting by compressed air are carbodies, furniture, articles made of plastic materials reinforced byincorporated fibreglass, boats, airplanes, leather articles in general,etc.

[0008] It is also known that in order to improve the painting quality,elimination of every impurity that may bind to the paint is required aswell as making drying of the laid-down paint film as more as possibleuniform and quick.

[0009] In this way, the possibilities that paint may absorb impuritiesand moisture from the compressed carrier air or even from ambient airare reduced, in particular if working takes place in an uncontrolledenvironment.

[0010] Therefore, in order to improve quality of painting, thecompressed-air flow is dried to remove the condensate (making the airpass through a low-temperature refrigeration-cycle drier for example,generally until a dew-point value not lower than +3° C.) and filtered toeliminate traces of oil or other impurities (by filtering the air bymeans of coalescence filters or activated-carbon filters, for example).

[0011] In the spray-painting technique referred to as HVLP (highvolumes, low pressure of the compressed air) also known is use of a flowof heated air for the purpose of accelerating paint drying and improvetransfer efficiency, i.e. exploitation of the paint employed.

[0012] Systems of known type however have some drawbacks due to the factthat different paints and surfaces may require different sprayconditions (in particular in terms of pressure and temperature of thecarrier fluid).

[0013] It is the same as regards environmental conditions, since forinstance work parameters may change to a great extent between a workingcarried out to a room temperature of +30° C. rather than of +5° C.

[0014] In addition, known systems are not always satisfactory when highpurity of the compressed air and a high drying degree are required.

[0015] At all events, the painting systems of known type have thedrawback that they are limited to use of air as the carrier fluid, andtherefore involve a problem of possible oxidation of the paints.

SUMMARY OF THE INVENTION

[0016] Accordingly, it is a first aim of the present invention topropose a spray-painting apparatus using treated air, adapted toeliminate the above mentioned drawbacks.

[0017] It is another aim to propose an apparatus and method forspray-painting devices, which have a high yielding and are quitereliable in terms of characteristics of the dry compressed air ormodified nitrogen-rich air, treated to the different temperatures.

[0018] It is a further aim to propose a spray painting apparatus ofversatile use and ready adaptation in which hollow-fibre membranes areused to treat the compressed air by drying it, or hollow-fibre membranesto obtain modified air rich in nitrogen are used alternatively or in aninterchangeable manner, in both cases being it possible to operate underdifferent pressure and temperature conditions.

[0019] Advantageously, a carrier fluid of nitrogen-rich air in aconcentration of nitrogen from 95 to 99.9% can be used for spraypainting according to the invention.

[0020] According to the invention, the temperature of the notroge-richetreated air can be adjuasted within the range of 5° to 60° C., obtaininga due point which can vary from −40C° and −80° C.

[0021] In this way, the treated air does not have oil impurities,humidity or other impurities which could be dangerous for the quality ofpainting.

[0022] Furthermore, the use of ananhydrous carrier fluid, which has highpurity and adjastable temperature irrespective of the room temperature,allows a quick reticulation process of bi-component paints and a quickevaporation of voilatile components.

[0023] As a result, the spraied paint is more stable and its drying ismore rapid and uniform.

[0024] A further aim of the present invention is to propose a method ofspray-painting capable of eliminating the drawbacks of known systems.

[0025] The foregoing and still further aims are achieved by an apparatusfor spray-painting comprising an inlet for air under pressure (AIR IN);a heating unit (G1) to heat the compressed air; an air-drying and/orseparation unit (G2) operating by means of hollow-fibre membranes; means(3, 15, 16) for adjusting heating of the treated air; means (13) foradjusting pressure of the treated air; means (10, 19) for regulation ofthe dew point should the unit (G2) comprise hollow-fibre membranes forair drying, and/or for regulation of the residual percentage of oxygenin the treated air should the unit (G2) comprise hollow-fibre membranesfor production of modified air rich in nitrogen; an outlet for thetreated air (AIR OUT) to be used as paint carrier fluid.

[0026] Also disclosed is a spray-painting method comprising the steps offeeding air under pressure; adjustably heating the air to be treated;treating the heated air by separation membranes to a preestablished andadjustable drying/separation degree; supplying the treated air to anadjusted pressure and temperature as carrier fluid for the paint.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further features and advantages of the invention will become moreapparent from the following detailed description of a preferredembodiment given by way of non-limiting example with the aid of theaccompanying drawings, in which:

[0028]FIG. 1 is a diagram of a first embodiment of the apparatus inaccordance with the invention;

[0029]FIG. 2 is a second embodiment of the apparatus of the invention;

[0030]FIG. 3 is a third embodiment of an apparatus in accordance withthe invention;

[0031]FIG. 4 shows a fourth embodiment of the apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] In accordance with the invention and with reference to theaccompanying drawings, a spray painting apparatus comprises:

[0033] an inlet for the air under pressure “AIR IN”;

[0034] a unit G2 for air treatment by means of hollow-fibre separationmembranes;

[0035] a heating unit G1 to heat the air, placed either upstream of unitG2 (FIGS. 1 and 2) or downstream of said unit (FIGS. 3 and 4);

[0036] a storage unit G3 for the treated air, which is optional and isfitted between the outlet unit G2 and the use. Unit G3 preferablycomprises a tank 20 with thermal insulation 21 to eliminate pressureoscillations at the exit following pulsations of the outgoing air duringpainting. Unit G3 can be inserted in a casing 26 preferably made of anextruded section member of aluminum, preferably of a cylindrical shapeor square section;

[0037] an outlet for the treated air “AIR OUT” to be used as carrierfluid of the paint;

[0038] a thermometer 11 to measure and display the temperature of theair entering unit G2;

[0039] a pressure meter 14 b to display and adjust the dried-airpressure produced by a pressure reducer 13;

[0040] a pressure meter 14 a to display and control pressure in tank G3,if provided;

[0041] a flow regulator 10 downstream of the membrane unit G2 to eitheradjust the dew point of the dried air produced by G2 or vary thenitrogen percentage in the treated air;

[0042] a temperature regulator 16 to adjust the temperature of the airentering the air-drying unit G2;

[0043] a unit 15 for control of the pre-heating unit G1 based onadjustment of regulator 16.

[0044] In more detail, the apparatus may further comprise:

[0045] a three-way valve 18 controlled by the electronic control unit 15and located upstream of the membrane unit G2 for exhaust of possiblecondensate;

[0046] a filtering unit 1 to filter the air under pressure to besupplied to the pre-heating unit G1;

[0047] instrumentation for control and operation;

[0048] a check-valve 2 for the air entering the preheating unit Gi;

[0049] a check-valve 19 for the air coming out of the membrane unit G2,after the flow regulator 10;

[0050] a pressure meter 12 a to gauge pressure of the air upstream ofthe filtering unit 1,

[0051] a pressure meter 12 b to gauge pressure of the air after thefiltering unit 1.

[0052] More specifically:

[0053] the pre-heating unit G1 consists of a coil 5 wound around aresistor 3 and housed within a casing 4 preferably made of an extrudedsection member of aluminum, preferably of cylindrical shape or squaresection.

[0054] Alternatively, in the manufacture of said unit G1 coil 5 may alsobe eliminated making casing 4 operate as a tank for the air to beheated.

[0055] Preferably, coil 5 is a tube of copper or aluminum of afloating-spiral type and resistor 3 is of the armored type having avarying temperature controlled by a control diode or an electronicmicroprocessor circuit.

[0056] The drying unit G2 comprises a casing 6 preferably consisting ofan extruded section member of aluminum, of cylindrical shape or squaresection for example, within which a membrane module 7 is housed for airdrying, which is supported inside casing 6 by a pair of rings 8.

[0057] Preferably, casing 6 is of a type adapted to be opened and module7 is of the interchangeable type so that it can be easily replaced,either by a nitrogen-separation module of same sizes for example or byanother air-drying module.

[0058] The control instrumentation may comprise, in addition tothermometer 11 and pressure meter 14 b, another pressure meter 14 a forcontrol of the air pressure in tank 20.

[0059] The filtering unit 1 is of the combined type, class 1 ISO 8573-1,to abate oil contents to values <0.001 mg/mc and oil vapor contents tovalues <0.003 mg/mc.

[0060] In operation (in the embodiment shown in FIGS. 1 and 2), thecompressed air passes through the filtering unit 1, goes beyond thecheck valve 2 and enters coil 5 at the inside of casing 4.

[0061] On coming out of coil 5, the air passes through the three-wayvalve 18 discharging possible condensate and enters the air-drying unit7 at the inside of casing 6.

[0062] Preferably, valve 18 operated by the electronic control unit 15enables air passage through the membrane only on reaching of apredetermined threshold temperature regulated by a thermostat 17.

[0063] In the membrane, if it is of the type suitable for drying, dryingof the air takes place, with dew-point values of the produced air thatmay range from 0° to −40° C.

[0064] The air from membrane 7 passes through the flow regulator 10,check valve 19 and subsequently the pressure reducer 13 and is stored ina storage chamber 20 ready for use, being for example destined to aspray-painting nozzle, passing through the pressure reducer 13.

[0065] In the embodiment shown in FIGS. 3 and 4, position of units G1and G2 is reversed, so that air heating takes place after treatment bymeans of the membranes.

[0066] The control instrumentation, possibly gathered in a panel 9,enables checking of:

[0067] the temperature value at the membrane entry (thermometer 11 a) towhich will correspond an exit temperature depending on cooling takingplace in the particular membrane used (usually from about 15° C. toabout 50° C.) measured by a thermometer 11 b;

[0068] pressure at the exit of the apparatus (pressure meter 14 b) andpressure at the exit of the filtering unit 1 (pressure meter 12 b).

[0069] Therefore, depending on the desired application and finaltemperature of the treated air, it will be sufficient to act onregulator 16 to modify, by the electronic control unit 15, temperatureof resistor 3 and consequently pre-heating of the air entering themembranes.

[0070] If the dew-point value is wished to be modified, it will beinstead sufficient to act on the flow regulator 10.

[0071] Finally, pressure reducer 13 will be acted upon, if pressure ofthe dried air is wished to be adjusted.

[0072] Should the membrane unit 7 consist of a module for production ofmodified air rich in nitrogen, the flow regulator 10 itself enablespurity of the produced nitrogen to be adjusted.

[0073] In addition, control and automatic adjustment of the operationvalues can be achieved by supplying the electronic control unit 15 withinitial setting values and using a feedback of the measured temperaturevalues at the entry or exit of the membranes, to automatically adaptheating of the air based on the temperature set value and thetemperature actual value.

[0074] Likewise, setting and adaptive control of the pressure values andvalues of other parameters can be provided, such as the drying degree ofthe treated air or purity of the produced nitrogen, when such values arewished to be maintained under control.

[0075] Shown in FIGS. 2 and 4 are embodiments of the apparatus in whichcasings 4, 6, 26 are superposed on each other and are all provided withlids 27, 28, 29 adapted to be opened to enable easy replacement of therespective units G1, G2, G3.

[0076] The apparatus may also comprise an on/off switch 22 forconnection to the electric power network, and signalers such as pilotlights 23 and 24 to signal a stand-by state and a production state ofthe apparatus respectively, and a counter to record the apparatus' workhours.

[0077] Advantageously, with an apparatus as shown in FIGS. 1 and 2 afurther advantage is achieved, i.e. the quality of the air for paintingis improved as well as efficiency of the air-drying/nitrogen-separationmembrane.

[0078] In fact, the drying/separation membranes have a maximumefficiency at about 56° C. to which corresponds a temperature at theexit of about 15° C. to 40° C., and it is exactly in the neighborhood of35° C. and 56° C. respectively, that the optimal values for many typesof painting and for efficiency of the membranes are.

[0079] At all events, these average values are to be intended by way ofexample, since the operation values may depart therefrom depending onthe type of membranes used and on the application of the apparatus.

[0080] Obviously many modifications and variations may be made to theapparatus as conceived, all of them falling within the inventive ideacharacterizing it. In particular, due to the use of hollow-fibremembranes, the apparatus may supply treated air to values that aresteady and adjustable both as regards temperature and pressure and asregards purity, in many other applications (medical applications, forexample).

1. A spray-painting apparatus comprising: an inlet for the air underpressure (AIR IN); a heating unit (GI) to heat the compressed air; anair-drying and/or separation unit (G2) operating by means ofhollow-fibre membranes; means (3, 15, 16) for adjusting heating of thetreated air; means (13) for adjusting pressure of the treated air; means(10, 19) for regulation of the dew point should the unit (G2) comprisehollow-fibre membranes for air drying, and/or for regulation of theresidual percentage of oxygen in the treated air should the unit (G2)comprise hollow-fibre membranes for production of modified air rich innitrogen; an outlet for the treated air (AIR OUT) to be used as paintcarrier fluid.
 2. The apparatus as claimed in claim 1, furthercomprising a thermometer (11) to measure and display the temperature ofthe air entering the unit (G2).
 3. The apparatus as claimed in claim 1,further comprising a pressure meter 14 b to display and adjust pressureof the treated air.
 4. The apparatus as claimed in claim 1, furthercomprising a three-way valve (18) upstream of the unit (G2).
 5. Theapparatus as claimed in claim 1, further comprising a filtering unit (1)for the air destined to the unit (G2).
 6. The apparatus as claimed inclaim 1, further comprising an instrumentation panel (9).
 7. Theapparatus as claimed in claim 1, further comprising a check valve (2)for the air entering the unit (G1).
 8. The apparatus as claimed in claim1, further comprising a check valve (19) for the air coming out of themembrane unit (G2).
 9. The apparatus as claimed in claim 5, furthercomprising a pressure meter (12) to gauge the air pressure upstream ofthe filtering unit (1).
 10. The apparatus as claimed in claim 1, whereinthe pre-heating unit (G1) is made up of a resistor (3) around which acoil (5) is wound for air passage, the resistor and coil being housedwithin a cylindrical casing (4).
 11. The apparatus as claimed in claim10, wherein the coil (5) is a tube of copper or aluminum of afloating-spiral type.
 12. The apparatus as claimed in claim 1, whereinthe pre-heating unit (G1) is made up of a resistor placed within acylindrical casing communicating with the air inlet and the unit (G2).13. The apparatus as claimed in claim 10, wherein the resistor (3) is ofthe armored type with a varying temperature.
 14. The apparatus asclaimed in claim 13, wherein the resistor (3) is controlled by a controldiode or an electronic microprocessor circuit.
 15. The apparatus asclaimed in claim 10, wherein said casing (4) consists of an extrudedsection member made of aluminum.
 16. The apparatus as claimed in claim11, wherein said means (3, 15, 16) for adjusting heating of the treatedair consists of a temperature regulator (16) of the air entering theunit (G2), and an electronic unit (15) for control of the resistor (3)of the heating unit (G1) based on adjustment of the regulator (16). 17.The apparatus as claimed in claim 1, wherein said means for adjustingpressure of the treated air consists of a pressure reducer (13)associated with the pressure meter (14).
 18. The apparatus as claimed inclaim 1, wherein said means for adjusting purity of the treated airconsists of a flow regulator (10) placed downstream of the membrane unit(G2).
 19. The apparatus as claimed in claim 1, wherein the unit (G2)comprises a casing (6) consisting of an extruded section member made ofaluminum, within which a membrane module (7) for air drying/separationis housed, which module is supported in the casing (6) by a pair ofrings (8).
 20. The apparatus as claimed in claim 19, wherein the casing(6) can be opened and the module (7) is of the interchangeable type sothat it can be easily replaced.
 21. The apparatus as claimed in anyoneof the preceding claims, wherein the panel (9) comprises the thermometer(11), pressure meter (14), pressure reducer (13), flow regulator (10),temperature regulator (16) and in addition another pressure meter (12)for control of the air pressure upstream of the filtering unit (1). 22.The apparatus as claimed in claim 5, wherein the filtering unit (1) isof the combined type class 1 ISO 8573-1, for oil contents <0.001 mg/mcand oil vapor contents <0.003 mg/mc.
 23. The apparatus as claimed inclaim 1, wherein said air-heating unit is placed upstream of-saidmembrane unit (G2).
 24. The apparatus as claimed in claim 1, whereinsaid air-heating unit is placed downstream of said membrane unit (G2).25. The apparatus as claimed in claim 1, comprising a storage unit (G3)for the treated air.
 26. The apparatus as claimed in claim 25, whereinsaid unit (G3) comprises a storage chamber (20) with a thermalinsulation (21).
 27. A spray-painting method comprising the followingsteps: feeding air under pressure; adjustably heating the air to betreated; treating the heated air by separation membranes to apreestablished and adjustable drying/separation degree; sprying thetreated air to an adjusted pressure and temperature as paint carrierfluid.
 28. The method as claimed in claim 27 in which said treatmentstep takes place by at least one membrane unit for air drying.
 29. Themethod as claimed in claim 27, wherein said treatment step takes placeby at least one hollow-fibre membrane unit to enrich the air withnitrogen for separation.
 30. The method as claimed in claim 28, whereinsaid step of drying the heated air is carried out until dew-point valuesof the treated air in the range of 0° to −40°.
 31. The method as claimedin claim 29, wherein said air-treating step is carried out untilair-purity values of 90-99.5% in nitrogen.
 32. The method as claimed inclaim 27, wherein said adjustable heating of the air fed, treatment ofthe heated air to a preestablished and adjustable drying/separationvalue and adjustment of the supplied air are automatically adapted basedon preestablished temperature, purity and pressure values of the air tobe supplied and on the measured temperature, purity and pressure valuesof the supplied air.
 33. The method as claimed in claim 27, wherein saidsupply of the treated air is carried out to an air temperature between15° C. and 50° C.
 34. A method of spray-painting comprising the stepsof: sending a jet under pressure of a carrier fluid for the paint to besprayed; mixing a paint flow with the jet of the carrier fluid underpressure; spraying the obtained mixture onto an object to be painted;wherein said carrier fluid consists of modified air rich in nitrogen.35. The method as claimed in claim 34, wherein said modified air isobtained by separation by means of hollow-fibre separation membranes.